This invention relates to a manual pushbutton keyboard system for an electronic pocket calculator, for a pushbutton telephone, or for other electrical or electronic appliances, and it is particularly concerned with such a keyboard which utilizes dished or domes disks as switch actuating elements of single-pole, single-throw (SPST) momentary switches for the keyboard.
More generally, calculator keyboards conventionally include a plurality of SPST momentary switches and a network of conductor paths on a printed circuit board leading to terminals at one margin of the board for connection of the keyboard switches to other electronic components, such as to various solid state, integrated circuit, and semi-conductor logic components within a calculator. Prior art keyboards, such as shown in the coassigned U.S. Pat. Nos. 3,684,842, 3,806,673 and 3,808,384, utilized domed disks as switch actuating elements. The disks in these prior art keyboards were conventionally retained in place relative to their respective contacts by means of an apertured retainer board having a thickness generally of the height of the domed disks, with the disks received in the apertures in the retainer board. This retainer board represented a substantial portion of the cost of the keyboard. The conductor paths in these prior art keyboards were constituted by chemically etching metal from one or both sides of a laminated insulative board in a preselected pattern. This so-called subtractive method of producing a printed circuit board is relatively slow and expensive and it poses certain ecological problems in the disposal of chemical wastes. Other keyboards are known in which disks are loosely retained in deeper recesses formed in a molded plastic substrate board. In this last-mentioned prior art keyboard, the conductor paths are applied to the substrate board by a well-known additive electroless plating process. However, the deep recesses posed a problem in plating the vertical surfaces of the recesses, and required the board to be relatively thick to accommodate the disks.